Awareness of this serious congenital heart defect got a big bump after the late-night host shared the story of his newborn son's diagnosis and open-heart surgery.

Kimmel choked up as he told the audience how, a few hours after baby Billy's relatively trouble-free delivery on April 21, a "very attentive" nurse detected a heart murmur (which is somewhat common in newborns) and observed that his skin appeared purple (which was not normal).

Later that night, a pediatric cardiologist diagnosed Billy with Tetralogy of Fallot (TOF) with pulmonary atresia, a severe variety of a combo pack of four related congenital heart defects named for Étienne-Louis Arthur Fallot, the French doctor who identified the disease's four defining traits in 1888.

TOF affects one in 2,500 newborns; the pulmonary atresia variety affects less than 20% of that number.

Children with TOF have all four cardiac defects in varying degrees but in Billy's case, the two most serious problems are a completely obstructed pulmonary valve or artery (atresia) and a hole between his left and right ventricles (ventricular septal defect).

"The pulmonary valve is the aspect that needs immediate attention," explains Dr. Nicolas Madsen, an assistant professor of pediatric cardiology at Cincinnati Children's Hospital and vice-chair of the Medical Advisory Board for the Pediatric Congenital Heart Association.

"Without flow through the pulmonary valve, there's only one other way for blood to get into the lungs, and that's through a blood vessel called the ductus arteriosus that's wide open during pregnancy to allow blood to skip the lungs, since the placenta provides all the oxygen. But once you're born and need all of the blood going to the lungs, that connection between the circulation goes away in the first few days of life."

That means time is of the essence. Doctors need to act in those first few days while the vessel is still operational. "Once that disappears, you have no way of getting blood to the lungs ... Without prompt intervention by a cardiac surgery team, (TOF) would be fatal."

Last week, Vaughn Starnes, a renowned pediatric cardiothoracic surgeon at Children's Hospital Los Angeles, performed open-heart surgery to open up Billy's pulmonary valve and correct the oxygenation problem. (You'll notice the baby's skin color is normal in this photo posted Tuesday by Kimmel's wife Molly McNearney.)

Kimmel said Billy will undergo a second surgery to repair the hole between his left and right ventricles before he's 6 months old. Madsen says the procedure has multiple purposes: preventing oxygenated blood that's intended for the rest of the body from spilling from the left ventricle through the hole to the right chamber and reducing pressure on the lungs, which left untreated can result in long-term damage.

"That's why you don't want to wait two or three years to close this hole, he says. "You want to do it sooner than later."

Billy will need a third procedure, a valve replacement, by the time he's a tween. That's because the first surgery opens the valve completely, which has good and bad effects, Madsen notes.

"You've got blood flow to the lungs, which is great, but now you don't have the valve closing behind it, so blood can wash backward," he says. "That's well-tolerated for a number of years but after a while, that backwashed blood adds to the normal amount in the right heart and it stretches the right ventricle. Once that begins to happen, we put in a replacement valve. That can either be done surgically or percutaneously (a needle puncture through the skin) in a cardiac cath lab."

Replacement valves (whether synthetic, bovine or porcine) do degrade over time and need replacing every 10 to 15 years, he adds. "For congenital heart disease, often we can make the condition much better and provide a circulation that allows for a normal life but they're never truly repaired. It's something that you constantly have to go back and re-evaluate. (Billy) will require expert cardiac care for the rest of his life."

Once he gets past the surgery to close the ventricular hole, Madsen predicts the Kimmels' doctors visits will dwindle to one or two a year, not including surgeries and follow-ups. Those appointments will include a number of tests, including EKGs, stress tests, cardiac MRIs and 24-hour heart-rhythm monitoring — "many of them either annually or every three to five years."

He says parents should be aware that pediatric cardiac patients can have neurodevelopmental challenges —ranging from ADHD to problems with executive function or social IQ. That's why many pediatric cardiology centers have their own specialized clinics to help families with early identification and therapy.

Madsen says that with proper care, "Billy can achieve all the things he wants, from athletic pursuits to school to relationships and work."

Just look at Olympic gold-medalist snowboarder Shaun White, 30, who was born with TOF and joined Kimmel for Monday's cardiac-themed episode.

In fact, Kimmel told the X-Games star that every time he told a friend or family member about Billy's diagnosis, they mentioned that White had the same thing, causing the comedian to whine, "My son's going to be a snowboarder?!?"